1. Field of the Invention
The present invention relates to an EL (Electroluminescence) display and a method of production thereof.
2. Description of Related Art
In recent years, attention has been given to an OLED (Organic Light Emitting Device) (“All About Organic EL”, by Junji Kido, published by Nippon Jitsugyo Publishing Co., Ltd., Feb. 20, 2003). The OLED is now used as a display of various products including mobile phones and digital cameras.
In applications of the well-known OLED to a full-color display, three main methods are available: (1) whole-surface white OLED and color filters, (2) whole-surface blue OLED and CCM (Color Changing Media), and (3) cells formed separately for R (Red), G (Green) and B (Blue). The RGB separate forming method, which has the highest emission efficiency and realizes a display high in color purity, has most advanced.
The RGB separate forming method includes a shadow mask method in which the cells are formed separately by evaporation using a metal mask (hereinafter, referred to as “mask”) 20 shown in FIG. 4 (“All About Organic EL”, by Junji Kido, published by Nippon Jitsugyo Publishing Co., Ltd., Feb. 20, 2003). Before the cells are separately formed, alignment marks on the mask 20 and a substrate 11 are measured with a CCD (Charge Coupled Device) camera, the shift of the mask 20 from the relative position is calculated by a computer, and the mask 20 is moved in accordance with the result of calculation. This is an alignment process. Normally, one alignment operation cannot produce a sufficiently high accuracy, and therefore several alignment operations are conducted. Thus, the process of attaching the mask 20 and a wall 14 closely to each other by a magnet and separating them from each other is repeated. As shown in FIG. 4, the mask 20 is set in position with respect to the substrate 11 in such a manner that all the pixel areas are open through holes 22 of the mask 20 at the time of evaporation.
In setting the mask 20 in position with respect to the substrate 11, as described above, the mask 20 closely attached to the wall 14 is separated from the wall 14 in some cases. In this process, the mask 20 and the wall 14 on the substrate 11 interfere with each other in some cases, and the mask 20 is caught by the wall 14 of the substrate 11, so that the wall 14 of the substrate 11 is scratched or the mask 20 itself is damaged in some cases. This is because the wall 14 in contact with the mask 20 is made of polymer; therefore, the contact angle of the polymer with water is so small as at several degrees to several tens of degrees and the wettability thereof is high. As another reason, in the case where the wall is formed of polymer not small in contact angle with water, the wettability of the wall is probably improved by oxygen plasma treatment or UV ozone treatment performed to clean an anode surface. Herein, the polymer making up the wall is a photosensitive negative resist.
Once the wall is scratched as described above, the display performance of the EL display is probably reduced. Also, the mask, if damaged, is required to be replaced, which consumes time and reduces the productivity while at the same time increasing the production cost of the EL display.
Once the wall is scratched as described above, the display performance of the EL display 10c is usually reduced. Also, the mask, if damaged, is required to be replaced, which consumes time and reduces the productivity while at the same time increasing the production cost of the EL display.
This invention has been achieved in view of the problems described above, and an object thereof is to prevent the wall from being scratched by the mask deposited by evaporation and also to prevent the mask from being damaged.